linux-kernel - Re: [PATCH] mm: huge_memory: don't force huge page alignment on 32 bit

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Message-ID: <bd9d782cbe5b7a80c929ff35c8b49f0036dda439.camel@decadent.org.uk>
Date: Thu, 11 Jul 2024 22:52:13 +0200
From: Ben Hutchings <ben@...adent.org.uk>
To: Yves-Alexis Perez <corsac@...ian.org>, Yang Shi <shy828301@...il.com>, 
 jirislaby@...nel.org, surenb@...gle.com, riel@...riel.com,
 willy@...radead.org,  cl@...ux.com, akpm@...ux-foundation.org
Cc: yang@...amperecomputing.com, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, Salvatore Bonaccorso <carnil@...ian.org>
Subject: Re: [PATCH] mm: huge_memory: don't force huge page alignment on 32
 bit

On Thu, 2024-07-11 at 22:10 +0200, Yves-Alexis Perez wrote:
> On Thu, 2024-01-18 at 05:35 -0800, Yang Shi wrote:
> > The commit efa7df3e3bb5 ("mm: align larger anonymous mappings on THP
> > boundaries") caused two issues [1] [2] reported on 32 bit system or compat
> > userspace.
> > 
> > It doesn't make too much sense to force huge page alignment on 32 bit
> > system due to the constrained virtual address space.
> 
> Hi people,
> 
> sorry for beeing so late. I've looked at this following the OpenSSH issue
> (CVE-2024-6387 [1]) and especially the impact on IA-32 installations where
> ASLR is apparently broken.
> 
> There was a recent thread [2] on oss-security discussing the issue.
> 
> Looking at the commit log I think the intention was to fix this both for:
> - 32 bit process running on 64 bit kernels: in_compat_syscall()
> - all processes running on 32 bit kernels: IS_ENABLED(CONFIG_32BIT)
> 
> Unfortunately, as far as I can tell, CONFIG_32BIT is not enabled on 32bit x86
> kernels. Maybe CONFIG_X86_32 would be the right one there?

CONFIG_64BIT appears to be defined and enabled in all 64-bit
architectures, so I think !IS_ENABLED(CONFIG_64BIT) would work as a
generic check.

Ben.

> 
> [1] https://www.openwall.com/lists/oss-security/2024/07/01/3
> [2] https://www.openwall.com/lists/oss-security/2024/07/08/3

-- 
Ben Hutchings
Computers are not intelligent.	They only think they are.


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